Is a relay a good choice....

Hey all,
I have a project in which in need to switch a low current control signal similar to an automotive ignition. I have to switch 5 control signals under different circumstances. So my question, should I use a latching relay or is there a component that is cheaper and smaller than a relay? I know SCRs can act as switched but the are more for switching current not signals...

Any help is appreciated!


To provide some guidance we need some additional information.

  1. What type of current are you expecting (estimated)? Around here an automotive ignition (a few amps maybe) is considered high current (or at least not low current).

  2. Do you have isolation or grounding limitations?

  3. Is power a consideration (i.e. are you using a battery)?

  4. What will be controlling these signals (Arduino etc)?

Off hand low current signals can be switched by MosFet's, OptoIsolators, Relays


Thanks for the reply, and to answer your questions..

  1. I est less than an amp.. this is a 24v system.

  2. No ground limitations

  3. Low power is good, since the project is controlling a remote start for a generator. The generator can be inactive for a bit before we run it and conserving battery is a good thing.

  4. Control will be via Arduino Uno.


Does the generator's starting system not work? What parts are still working?


Went to school many many years ago, I like relays for applications that don’t require constant switching.

They give 100% isolation too.

I personally would consider a MosFet before a relay (assuming the control circuit will accept an switch to ground).

My reason is failure mode, with the MosFet if the Arduino goes off line it can be designed to “default” to a safe mode for your system.

Also the MosFet consumes almost no power to operate. I realize a latching relay draws no power.

Perhaps you could let us know what you have to switch. i.e. a control voltage (24V) to ground? Or supply 24V to another device etc.

3) Is power a consideration (i.e. are you using a battery)?

Just a note on clarity of communication: the term "power" can mean any kind of power--battery, mains, back-up generator, solar panel, etc.. Sounds like you're using it, here, as shorthand for "mains power", judging by the qualifier ("i.e. are you using a battery").

Judging by the lack of the OP's acknowledgement on the topic of mains power, I would say there was a lack of comprehension.
It's like saying "I received a call". A call on what, a radio, a telephone, an intercom, a smoke signal? Normally, the context will sort it out: a John Ford western: smoke signal--a boat out at sea: marine radio--a Tudball/Wiggins Burnett sketch: intercom--etc.

The context, here on this Forum, is not always so clear. Just something to consider.

[who refers to a smoke signal as "receiving a call"?!?]

I did comprehend his shorthand, it was obvious, but thank you for your input.

I did comprehend his shorthand, it was obvious, but thank you for your input.

Cool. And, here's my 2¢
A proper answer, truly, as JohnRob pointed out, requires more information from the OP, but:

  • If the OP is inexperienced, a relay might be a simpler, direct avenue to success [unless the amount of current being switched is greater than, around 2A, in which case, the amount of current needed to drive the Relay may be too much for an Arduino output (20mA conservative, 40mA max)]. Also, be sure to include a freewheeling diode [such as a 1N4148, across the relay coil, such that the cathode is connected to the positive supply. 1N4148 will work for coil currents less than around **1A. **If higher currents are involved, then select a beefier fast-recovery diode] -- also known as a flyback diode, snubber diode, suppressor diode, catch diode, clamp diode, or commutating diode].
  • Otherwise, if it's a DC "signal" [i.e. the polarity never reverses - like in the case of AC], then a MOSFET is probably the best solution. The "latching" function can be provided by the Arduino. Best to include a resistor in series with the Gate [140Ω for 5V drive and 100Ω if 3.3V]. Also, if you are switching anything involving inductance, then include some sort of protection, like the 1N4148 described above. Also, a pull-down resistor on the Arduino output pin is not a bad idea -- around 100k should suffice.
  • If the Arduino needs to be isolated from whatever it is you're switching, then consider an Opto-Isolator. And, the Opto-Isolator will probably need to drive a Power MOSFET [that will handle the full current], since you probably won't find an idolator that can handle the current involved.
  • Another possibility is a Solid State Relay [SSR].